[Coco] Max Video Resolution

[Mark McDougall]

On 4/01/2017 3:57 AM, Glen Hewlett wrote:

> I’m at the point in my Z80 Pac Man translation to 6809 and I am stuck
> trying to figure out the best way to deal with the rotated screen of
> the original Pac Man.  What I need is screen resolution that is
> 320x256.  Over the years has anyone found any hidden graphics modes
> to give you more rows then the documented 320x225?

If you saw my Pacman project photos for the Model 4, you'll see that I 
had a similar problem (640x240), and I didn't even realise it until I'd 
gotten a little further into it! Unfortunately scrolling on that 
hardware is not an option. :(

I'm assuming you're rotating the screen to show it in the correct 
orientation; ie. 28x32 tiles or 224x256 pixels for the maze, and 
displaying the other 4 rows of text/icons on the RHS of the screen like 
pretty much every other console port in the history of consoles?!? ;)

I notice Nick's Pacman page mentions "the tallest vertical resolution I 
could muster... 320x225 pixels" so unless he or others have learned more 
since, I guess that's it?!? The GIME register reference also suggests 
225 is the limit...

> If not I’m either going to have to shrink all the character data from
> 8x8 to 7x7. The other thing I’ve thought of is scrolling the screen
> vertically, so that if you are in the top half of the screen you will
> see everything but the 4 character rows at the bottom and vice versa
> if you are at the bottom of the screen.  This will also mess with any
> score or level info I might have on the right of the Maze though.  I
> really need a bigger screen.

I'm assuming Nick shrunk the character data to 7 pixels; I'd be tempted 
to keep it at 8x7 or your screen calcs and tile/sprite data will be 
worse than the Apple II! ;)

Scrolling is not a bad idea, even if you implement that as a 1st-pass 
(it will be a lot easier) and a novel approach to the game. You could 
use a similar display to Nick's, but more centered, and all info should 
still be visible whilst scrolling.

I have actually done exactly this for an FPGA implementation I did for 
Pacman to run on a 320x240 LCD (on the terASIC DE2) many years ago. It 
was a quick hack of the standard VGA version (of course the method has 
absolutely no relevance to a software implementation) but the point is, 
it was still quite playable. Of course it was a slightly different 
experience as sometimes one or more of the ghosts weren't visible, plus 
you couldn't immediately see how many dots or power pills you had left. 
But again, I think worth tackling first since it would be a relatively 
small enhancement to a non-scrolling display of 8x8 tiles that simply 
cut off the bottom edge. From there you could decide whether 8x7/7x7 was 
worth the effort?!?

Very interested to see your results!

Regards,

-- 
Mark McDougall
<http://retroports.blogspot.com.au>